US8907674B2 - System and method for determining degradation of rechargeable lithium ion battery - Google Patents
System and method for determining degradation of rechargeable lithium ion battery Download PDFInfo
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- US8907674B2 US8907674B2 US13/700,604 US201113700604A US8907674B2 US 8907674 B2 US8907674 B2 US 8907674B2 US 201113700604 A US201113700604 A US 201113700604A US 8907674 B2 US8907674 B2 US 8907674B2
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- lithium ion
- ion battery
- rechargeable lithium
- capacity
- degradation
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/385—Arrangements for measuring battery or accumulator variables
- G01R31/387—Determining ampere-hour charge capacity or SoC
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- G01R31/3634—
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/48—Accumulators combined with arrangements for measuring, testing or indicating the condition of cells, e.g. the level or density of the electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/54—Reclaiming serviceable parts of waste accumulators
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- G01R31/3679—
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/36—Arrangements for testing, measuring or monitoring the electrical condition of accumulators or electric batteries, e.g. capacity or state of charge [SoC]
- G01R31/392—Determining battery ageing or deterioration, e.g. state of health
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M2010/4292—Aspects relating to capacity ratio of electrodes/electrolyte or anode/cathode
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y02E60/12—
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/60—Other road transportation technologies with climate change mitigation effect
- Y02T10/70—Energy storage systems for electromobility, e.g. batteries
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- Y02T10/7011—
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/84—Recycling of batteries or fuel cells
Definitions
- the present invention relates to a system and method for determining degradation of a rechargeable lithium ion battery, and more specifically, diagnosing how a rechargeable lithium ion battery is degraded for determining whether the battery is reusable/recyclable.
- a rechargeable lithium ion battery is increasingly used as a power supply for driving motors of electric vehicles and hybrid vehicles or a power supply for portable devices.
- an electrically powered vehicle e.g. an electric vehicle and a hybrid vehicle
- it is used in the form of a plurality of packed cells (or a battery pack) in order to ensure required output voltage and a required amount of accumulated electric power, which invites a relatively high battery price.
- an electrically powered vehicle e.g. an electric vehicle and a hybrid vehicle
- it is used in the form of a plurality of packed cells (or a battery pack) in order to ensure required output voltage and a required amount of accumulated electric power, which invites a relatively high battery price.
- reusing/recycling the battery is an important issue in terms of cost
- diagnosing the battery's degradation to determine whether the battery is reusable/recyclable is an important technique.
- Japanese Patent Laying-Open No. 2003-7348 (PTL 1) describes a battery provision system and method characterized by determining whether a used battery is degraded.
- PTL 1 describes a system in which whether a rechargeable battery is degraded is determined and in accordance therewith if the battery is continuously usable it is recharged and resold by a distributor, otherwise it is sent from the distributor to its manufacturer and thus recycled.
- Japanese Patent Laying-Open No. 09-232008 describes a method of recycling a nonaqueous electrolyte used for various types of batteries including a lithium secondary battery.
- PTL 2 describes a method in which activated carbon is added to a nonaqueous electrolyte and they are agitated together and then left for a required period of time and thereafter an added liquid is filtered to remove the activated carbon for recovery. This can remove a substance that is a cause of degradation in the added liquid that is adsorbed by the activated carbon to recover the electrolyte from degradation.
- Japanese Patent Laying-Open No. 2008-241246 (PTL 3) describes a device based on a battery model expression to estimate a state on-line to estimate a state of a rechargeable battery.
- the document describes that the state estimation device has a characteristics map previously prepared of how a parameter in the battery model expression varies in value from that before use as the battery's state varies, and while the rechargeable battery is in use the device determines a parameter based on the battery model expression and obtains a ratio of the value of the determined parameter to that of the parameter before use corresponding to the battery's current state, (i.e., a rate of change) and diagnoses degradation of the battery.
- Japanese Patent Laying-Open No. 2009-63555 (PTL 4) describes whether a rechargeable lithium ion battery mounted in an externally rechargeable vehicle has lithium deposited therein is determined based on reduction of externally electrically charged full charge capacity. PTL 4 further describes that if it is determined that there is deposition of lithium, then, electrically charging/discharging the rechargeable lithium ion battery is restricted in using the battery. Furthermore, Japanese Patent Laying-Open No. 2009-199936 (PTL 5) describes that how many times a lithium secondary battery is electrically charged, how long it is operated, and other similar usage history information are referred to to calculate an amount of lithium deposited in the battery on the negative electrode. PTL 5 further describes starting controlling based on an amount of lithium deposited, as calculated, to dissolve and thus remove dendrite.
- PTLs 1 and 2 do not refer to that in recycling a rechargeable battery, whether the rechargeable battery's degraded state is within a recyclable range is determined before the battery has its cells disassembled. Accordingly, it is not before the cells are disassembled and thereafter chemically analyzed or the like that whether the rechargeable battery has an unrecyclablly degraded state is determined, and the disassembly and chemical analysis may invite a wastefully increased recycling cost.
- PTL 5 describes using a usage history of a rechargeable lithium ion battery to calculate an amount of lithium deposited therein.
- the usage history used is only the information of how many times the battery is electrically charged, the information of how many times the battery is electrically charged rapidly, the information of how many times the battery is fully electrically charged, and the information of a period of time for which the battery is operated, and the amount of lithium deposited therein is calculated from a regression using these items of information as variables. This is not an estimation based on the battery's actual voltage, current, temperature and the like and thus may not ensure that the amount of lithium deposited is estimated with sufficient precision, and appropriate determination of degradation may not be done.
- the present invention has been made to solve such a disadvantage and an object of the present invention is to determine whether a degraded rechargeable lithium ion battery is reusable/recyclable, based on an estimation of an amount of lithium deposited therein, nondestructively without disassembling the battery and appropriately.
- the present invention in one aspect provides a system for determining degradation of a rechargeable lithium ion battery, including a degradation parameter acquisition unit, a lithium deposition estimation unit and a determination unit.
- the degradation parameter acquisition unit is configured to perform a degradation diagnosis based on an open circuit voltage characteristic of the rechargeable lithium ion battery indicating how the rechargeable lithium ion battery varies in open circuit voltage as the battery varies in capacity to obtain a capacity ratio of a positive electrode of the rechargeable lithium ion battery, a capacity ratio of a negative electrode of the rechargeable lithium ion battery, and a battery capacity fluctuation amount.
- the lithium deposition estimation unit is configured to apply the capacity ratios respectively of the positive and negative electrodes that are obtained to a previously obtained correspondence between the capacity ratios respectively of the positive and negative electrodes and a first amount of the battery capacity fluctuation amount to separate the battery capacity fluctuation amount that is obtained into the first amount and a second amount of the battery capacity fluctuation amount the first amount corresponding to degradation attributed to wear, the second amount corresponding to degradation attributed to deposition of lithium.
- the determination unit is configured to determine whether the rechargeable lithium ion battery is reusable/recyclable based on at least one of: the capacity ratios respectively of the positive and negative electrodes obtained by the degradation parameter acquisition unit; and the second amount calculated by the lithium deposition estimation unit.
- the capacity ratio of the positive electrode is represented by a ratio of a capacity of the positive electrode with the rechargeable lithium ion battery in a degraded state to a capacity of the positive electrode with the rechargeable lithium, ion battery in an initial state.
- the capacity ratio of the negative electrode is represented by a ratio of a capacity of the negative electrode with the rechargeable lithium ion battery in the degraded state to a capacity of the negative electrode with the rechargeable lithium ion battery in the initial state.
- the battery capacity fluctuation amount is indicated by a product of the capacity of the negative electrode in the degraded state and an amount of a deviation of an axis of a composition of the negative electrode relative to an axis of a composition of the positive electrode in the degraded state.
- the determination unit is configured to determine whether the negative electrode of the rechargeable lithium ion battery is reusable/recyclable based at least on the second amount calculated by the lithium deposition estimation unit, and the determination unit is also configured to determine whether the positive electrode of the rechargeable lithium ion battery is reusable/recyclable based at least on the capacity ratio of the positive electrode obtained by the degradation parameter acquisition unit.
- the determination unit is configured to compare the second amount obtained by the lithium deposition estimation unit with a predetermined determination value to determine whether the negative electrode of the rechargeable lithium ion battery has a recyclable material.
- the determination unit is configured to determine whether the rechargeable lithium ion battery is reusable/recyclable based on comparison between at least one of the capacity ratio of the positive electrode, the capacity ratio of the negative electrode and the second amount, and a predetermined determination value.
- the determination value includes a first determination value for determining whether the rechargeable lithium ion battery is reusable, and a second determination value for determining whether the rechargeable lithium ion battery has an electrode with a recyclable material.
- the determination unit determines that the rechargeable lithium ion battery is reusable when it is determined that the positive electrode and the negative electrode are both reusable/recyclable in accordance with a determination of reusability/recyclability with the first determination value used, and the determination unit determines whether the positive electrode and the negative electrode are recyclable individually in accordance with the determination of reusability/recyclability with the second determination value used.
- the determination unit is configured to generate information based on a relationship in magnitude between the first and second amounts calculated by the lithium deposition estimation unit to indicate a climate condition suitable for reusing the rechargeable lithium ion battery.
- the determination unit is configured to generate information based on the second amount calculated by the lithium deposition estimation unit to indicate whether it is necessary to perform a process of removing deposited lithium in recycling a material of the negative electrode of the rechargeable lithium ion battery.
- the degradation parameter acquisition unit includes a measurement unit and a parameter searching unit.
- the measurement unit is configured to measure the open circuit voltage characteristic, by sensing a voltage and a current output by the rechargeable lithium ion battery as the rechargeable lithium ion battery is electrically charged and discharged and accordingly varies in capacity.
- the parameter searching unit is configured to determine the open circuit voltage characteristic that allows a minimum voltage error and a minimum capacity error for the open circuit voltage characteristic that is measured by the measurement unit while the capacity ratio of the positive electrode, the capacity ratio of the negative electrode, and the battery capacity fluctuation amount are varied to search for the capacity ratio of the positive electrode of the rechargeable lithium ion battery, the capacity ratio of the negative electrode, and the battery capacity fluctuation amount of the rechargeable lithium ion battery.
- the rechargeable lithium ion battery is mounted in an electrically powered vehicle configured to be externally electrically chargeable by a power supply external to the vehicle, and the measurement unit measures the open circuit voltage characteristic when the vehicle is externally electrically charged.
- the rechargeable lithium ion battery is mounted in an electrically powered vehicle including a hybrid vehicle, and the measurement unit measures the open circuit voltage characteristic by using: the open circuit voltage sensed as based on the voltage output when the rechargeable lithium ion battery is in a relaxed state; and how the battery varies in capacity, as sensed as based on an integral of the current output during each relaxed state.
- the measurement unit and the parameter searching unit are configured by a control unit mounted in the electrically powered vehicle for managing and controlling electrically charging and discharging the rechargeable lithium ion battery, and the degradation parameter acquisition unit communicates with the control unit to obtain the capacity ratio of the positive electrode, the capacity ratio of the negative electrode, and the battery capacity fluctuation amount.
- the present invention in another aspect provides a method for determining degradation of a rechargeable lithium ion battery, including the steps of performing a degradation diagnosis based on an open circuit voltage characteristic of the rechargeable lithium ion battery indicating how the rechargeable lithium ion battery varies in open circuit voltage as the battery varies in capacity to obtain a capacity ratio of a positive electrode of the rechargeable lithium ion battery, a capacity ratio of a negative electrode of the rechargeable lithium ion battery, and a battery capacity fluctuation amount; applying the capacity ratios respectively of the positive and negative electrodes that are obtained to a previously obtained correspondence between the capacity ratios respectively of the positive and negative electrodes and a first amount of the battery capacity fluctuation amount to separate the battery capacity fluctuation amount that is obtained into the first amount and a second amount of the battery capacity fluctuation amount, the first amount corresponding to degradation attributed to wear, the second amount corresponding to degradation attributed to deposition of lithium; and determining whether the rechargeable lithium ion battery is reusable/recyclable based on at least one of: the
- the capacity ratio of the positive electrode is represented by a ratio of a capacity of the positive electrode with the rechargeable lithium ion battery in a degraded state to a capacity of the positive electrode with the rechargeable lithium ion battery in an initial state.
- the capacity ratio of the negative electrode is represented by a ratio of a capacity of the negative electrode with the rechargeable lithium ion battery in the degraded state to a capacity of the negative electrode with the rechargeable lithium ion battery in the initial state.
- the battery capacity fluctuation amount is indicated by a product of the capacity of the negative electrode in the degraded state and an amount of a deviation of an axis of a composition of the negative electrode relative to an axis of a composition of the positive electrode in the degraded state.
- the step of determining includes the steps of: determining whether the negative electrode of the rechargeable lithium ion battery is reusable/recyclable based at least on the second amount obtained in the step of applying; and determining whether the positive electrode of the rechargeable lithium ion battery is reusable/recyclable based at least on the capacity ratio of the positive electrode obtained.
- the step of determining includes the step of comparing the second amount obtained in the step of applying with a predetermined determination value to determine whether the negative electrode of the rechargeable lithium ion battery has a recyclable material.
- the step of determining includes determining whether the rechargeable lithium ion battery is reusable/recyclable based on comparison between at least one of the capacity ratio of the positive electrode, the capacity ratio of the negative electrode and the second amount, and a predetermined determination value.
- the determination value includes a first determination value for determining whether the rechargeable lithium ion battery is reusable, and a second determination value for determining whether the rechargeable lithium ion battery has an electrode with a recyclable material.
- the step of determining includes determining that the rechargeable lithium ion battery is reusable when it is determined that the positive electrode and the negative electrode are both reusable/recyclable in accordance with a determination of reusability/recyclability with the first determination value used, and also determining whether the positive electrode and the negative electrode are recyclable individually in accordance with the determination of reusability/recyclability with the second determination value used.
- the step of determining includes the step of generating information based on a relationship in magnitude between the first and second amounts obtained in the step of applying to indicate a climate condition suitable for reusing the rechargeable lithium ion battery.
- the step of determining includes the step of generating information based on the second amount obtained in the step of applying to indicate whether it is necessary to perform a process of removing deposited lithium in recycling a material of the negative electrode of the rechargeable lithium ion battery.
- the step of performing includes the steps of measuring the open circuit voltage characteristic by sensing a voltage and a current output by the rechargeable lithium ion battery as the rechargeable lithium ion battery is electrically charged and discharged and accordingly varies in capacity; and determining the open circuit voltage characteristic that allows a minimum voltage error and a minimum capacity error for the open circuit voltage characteristic that is measured while the capacity ratio of the positive electrode, the capacity ratio of the negative electrode, and the battery capacity fluctuation amount are varied to search for the capacity ratio of the positive electrode, the capacity ratio of the negative electrode, and the battery capacity fluctuation amount of the rechargeable lithium ion battery.
- the rechargeable lithium ion battery is mounted in an electrically powered vehicle configured to be externally electrically chargeable by a power supply external to the vehicle, and the step of measuring includes measuring the open circuit voltage characteristic when the vehicle is externally electrically charged.
- the rechargeable lithium ion battery is mounted in an electrically powered vehicle including a hybrid vehicle, and the step of measuring includes measuring the open circuit voltage characteristic by using: the open circuit voltage sensed as based on the voltage output when the rechargeable lithium ion battery is in a relaxed state; and how the battery varies in capacity, as sensed as based on an integral of the current output during each relaxed state.
- the step of measuring and the step of determining the open circuit voltage characteristic are performed by a control unit mounted in the electrically powered vehicle for managing and controlling electrically charging and discharging the rechargeable lithium ion battery, and the step of performing includes communicating with the control unit to obtain the capacity ratio of the positive electrode, the capacity ratio of the negative electrode, and the battery capacity fluctuation amount.
- the present invention thus allows whether a degraded rechargeable lithium ion battery is reusable/recyclable to be determined, based on an estimation of an amount of lithium deposited therein, nondestructively without disassembling the battery and appropriately.
- FIG. 1 is a schematic block diagram showing a configuration of a system for determining degradation of a rechargeable lithium ion battery according to an embodiment of the present invention.
- FIG. 2 is a functional block diagram of a function to determine degradation of a rechargeable lithium ion battery according to an embodiment of the present invention.
- FIG. 3 conceptually represents a characteristic of how open circuit voltage varies with local state of charge (SOC).
- FIG. 4 is a graph schematically showing how a single electrode's open circuit potential varies as its capacity decreases.
- FIG. 5 is a conceptual diagram schematically representing a relationship between a deviation of a correspondence in composition between a positive electrode and a negative electrode, and their open circuit potentials.
- FIG. 6 is a schematic diagram for illustrating a deviation of a correspondence in composition caused by degradation.
- FIG. 7 is a figure for illustrating a degradation parameter when an unused rechargeable lithium ion battery's open circuit voltage curve as estimated is brought to coincide with that as measured.
- FIG. 8 is a figure for illustrating a degradation parameter when an open circuit voltage curve (as estimated) is brought to coincide with an open circuit voltage curve (as measured) in a case where degradation attributed to deposition of lithium is alone caused.
- FIG. 9 is a figure for illustrating a degradation parameter when an open circuit voltage curve (as estimated) is brought to coincide with an open circuit voltage curve (as measured) in a case where degradation attributed to wear is alone caused.
- FIG. 10 represents a relationship between positive and negative electrodes' capacity ratios and a capacity corresponding to a deviation of a correspondence in composition between the electrodes when degradation attributed to wear is alone caused.
- FIG. 11 is a flowchart representing a procedure of a process for determining degradation of a rechargeable lithium ion battery according to an embodiment of the present invention.
- FIG. 12 is a flowchart specifically showing a procedure of a process for determination of reusability/recyclability for a negative electrode of a rechargeable lithium ion battery.
- FIG. 13 is a flowchart specifically showing a procedure of a process for determination of reusability/recyclability for a positive electrode of a rechargeable lithium ion battery.
- FIG. 14 is a table for illustrating an example of determining reusability in determining degradation of a rechargeable lithium ion battery according to an embodiment of the present invention.
- FIG. 15 is a block diagram showing a system for measuring an open circuit voltage characteristic of a rechargeable lithium ion battery off board.
- FIG. 16 is a flowchart showing a procedure of a controlling process for obtaining a degradation parameter of a rechargeable lithium ion battery off board.
- FIG. 17 is a conceptual diagram for describing a process causing an open circuit voltage curve (as estimated) to coincide with an open circuit voltage curve (as measured).
- FIG. 18 is a flowchart showing a procedure of a controlling process for obtaining a degradation parameter of a rechargeable lithium ion battery that is mounted in a vehicle on board.
- FIG. 19 is a figure representing an error voltage between an open circuit voltage curve (as estimated) and an open circuit voltage curve (as measured).
- FIG. 20 is a figure showing an error voltage between an open circuit voltage curve (as estimated) and open circuit voltage.
- FIG. 21 is a flowchart showing a procedure of a process for illustrating an additional example of determining whether a rechargeable lithium ion battery is reusable in determining degradation of the battery according to a third embodiment of the present invention.
- FIG. 22 is a flowchart showing a procedure of a controlling process in determining degradation of a rechargeable lithium ion battery for determining whether the battery has a recyclable negative electrode according to the third embodiment.
- FIG. 1 is a schematic block diagram showing a configuration of a system for determining degradation of a rechargeable lithium ion battery according to an embodiment of the present invention.
- the present degradation determination system includes a rechargeable lithium ion battery 10 subject to determination of degradation, a battery sensor 15 provided at rechargeable lithium ion battery 10 , an electronic control unit (ECU) 20 for monitoring and controlling a state of charge of rechargeable lithium ion battery 10 , and a battery checker 30 .
- ECU electronice control unit
- Rechargeable lithium ion battery 10 has a positive electrode terminal 11 and a negative electrode terminal 12 .
- rechargeable lithium ion battery 10 shows a unit subject to determination of degradation. That is, rechargeable lithium ion battery 10 may be a unit cell, or may be a battery block formed of a plurality of unit cells connected, or a battery pack packed with accessories in one piece.
- the battery pack has a plurality of rechargeable lithium ion batteries electrically connected in series.
- the battery pack may internally include rechargeable lithium ion batteries electrically connected in parallel.
- Battery sensor 15 generically indicates a voltage sensor, a current sensor, and a temperature sensor, for example, and it is configured to sense the voltage, current, and temperature of rechargeable lithium ion battery 10 .
- ECU 20 is configured to monitor and control a state of charge of rechargeable lithium ion battery 10 on board, based on the battery's temperature, voltage, and current sensed by battery sensor 15 when the battery is in use. For example ECU 20 estimates a state of charge (typically, an SOC that is represented by a ratio of a currently available capacity to a full charge capacity) of rechargeable lithium ion battery 10 on board when the battery is in use. Alternatively, ECU 20 may set an upper limit for electric power to be charged/discharged based on an SOC, the battery's temperature, and the like as estimated, as occasion requires.
- a state of charge typically, an SOC that is represented by a ratio of a currently available capacity to a full charge capacity
- ECU 20 can also diagnose variation of internal resistance and other similar degradation in parallel while rechargeable lithium ion battery 10 is used, i.e., on board.
- ECU 20 can be configured to diagnose degradation on board and obtain a variety of degradation parameters on board and also record them, as done by the state estimation device described in Japanese Patent Laying-Open No. 2008-241246 (PTL 3).
- the degradation parameters include a diffusion coefficient Ds (diffusion resistance) in an active material of each electrode, direct-current resistance, and the like.
- determining degradation of rechargeable lithium ion battery 10 involves battery checker 30 , which includes a microprocessing unit (MPU) 31 , a memory 32 , and a communication device 33 .
- MPU microprocessing unit
- determination of degradation of rechargeable lithium ion battery 10 based on a degradation parameter obtained through a diagnosis of degradation on board or off board, determines whether rechargeable lithium ion, battery 10 is reusable/recyclable.
- on board shall indicate a scene in which rechargeable lithium ion battery 10 is used to operate a load (as shown in the figure), and “off board” shall indicate a scene after rechargeable lithium ion battery 10 used when the battery is evaluated by battery checker 30 and the like. Accordingly, on hoard, while ECU 20 operates with rechargeable lithium ion battery 10 , battery checker 30 will not be used.
- MPU 31 can read a program, data, and the like previously stored in memory 32 to perform a predetermined controlling process accompanied by an operation.
- Communication device 33 is configured to be capable of wired/wireless data communication with ECU 20 .
- Battery checker 30 thus communicating with ECU 20 via communication device 33 can read from ECU 20 a degradation parameter estimated by ECU 20 on board when rechargeable lithium ion battery 10 is in use.
- battery checker 30 can use a charging/discharging device (not shown) for tentatively electrically charging/discharging rechargeable lithium ion battery 10 to diagnose degradation of rechargeable lithium ion battery 10 off board.
- the rechargeable lithium ion battery can have positive electrode terminal 11 and negative electrode terminal 12 electrically connected to test terminals 35 and 36 to diagnose degradation of rechargeable lithium ion battery 10 off board.
- rechargeable lithium ion battery 10 can be electrically charged/discharged by a charging/discharging device (not shown). Then, battery checker 30 can use data measured in electrically charging/discharging the battery off board and follow a procedure of a process previously stored as a program to diagnose degradation.
- FIG. 2 is a functional block diagram of a function to determine degradation of a rechargeable lithium ion battery according to the present embodiment of the present invention.
- FIG. 2 shows functional blocks, which can be implemented for example by MPU 31 performing a predetermined programmed process.
- a degradation parameter acquisition unit 40 obtains a degradation parameter through an on or off board diagnosis of degradation of rechargeable lithium ion battery 10 .
- This degradation parameter shall include, as will be described in detail later, a positive electrode's capacity ratio k 1 defined by a ratio of the positive electrode's capacity in a degraded state to that in an initial state and a negative electrode's capacity ratio k 2 defined by a ratio of the negative electrode's capacity in a degraded state to that in an initial state, and a deviated capacity ⁇ Qs corresponding to a deviation of a correspondence in composition between the positive electrode and the negative electrode. Deviated capacity ⁇ Qs corresponds to a “battery capacity fluctuation amount”.
- the degradation parameters may also include the direct-current resistance and diffusion coefficient Ds indicated in PTL 3.
- a lithium deposition estimation unit 50 uses the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and an amount of battery capacity fluctuation (or deviated capacity) ⁇ Qs that are obtained by degradation parameter acquisition unit 40 to calculate a deviated capacity ⁇ Qs(Li) resulting from deposition of lithium in rechargeable lithium ion battery 10 at the negative electrode.
- ⁇ Qs(Li) has a value quantitatively indicating an amount of lithium deposited on the negative electrode.
- Determination unit 60 uses at least one of deviated capacity ⁇ Qs(Li) corresponding to deposition of lithium as obtained by the lithium deposition estimation unit, the positive electrode's capacity ratio k 1 and the negative electrode's capacity ratio k 2 to determine whether rechargeable lithium ion battery 10 is reusable/recyclable and also generate information on the battery's reusability/recyclability as determined. This determination can also be done using a degradation parameter other than the above (e.g., diffusion coefficient Ds).
- a degradation parameter other than the above e.g., diffusion coefficient Ds
- the information of the determination generated in determination unit 60 includes information on whether rechargeable lithium ion battery 10 is recyclable and/or information on whether the battery is reusable.
- “recycle” means disassembling rechargeable lithium ion battery 10 and recovering an electrode and other materials to use them again
- “reuse” means avoiding disassembling a unit cell and instead reusing the unit cell, a battery block or a battery pack as it is, or for example replacing a unit cell with another one and thus re-packing it to use it again as a battery pack.
- the degradation parameters used in determination on degradation in the present embodiment i.e., the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and battery capacity fluctuation amount (or deviated capacity) ⁇ Qs, will be described below more specifically.
- rechargeable lithium ion battery 10 includes a negative electrode, a separator including an electrolyte, and a positive electrode (not shown).
- the negative electrode and the positive electrode are each configured of an aggregate of spheres of an active material.
- a chemical reaction is caused on an interface of the active material of the negative electrode to discharge lithium ions Li + and electrons e ⁇ .
- a chemical reaction is caused on an interface of the active material of the positive electrode to absorb lithium ions Li + and electrons e ⁇ .
- the rechargeable lithium ion battery is electrically charged, a reaction opposite to the above reaction is caused.
- the negative electrode is provided with a current collector plate absorbing electrons and the positive electrode is provided with a current collector plate discharging electrons.
- the current collector plate of the negative electrode is formed for example of copper and connected to a negative electrode terminal.
- the current collector plate of the positive electrode is formed for example of aluminum and connected to a positive electrode terminal. Lithium ions are provided and received between the positive electrode and the negative electrode via the separator to electrically charge/discharge the rechargeable lithium ion battery.
- the rechargeable lithium ion battery internally has a state of charge varying with a lithium concentration profile in the active material of each of the positive and negative electrodes. This lithium contributes to a reaction of the rechargeable lithium ion battery.
- Resistance R includes pure electric resistance against electron transfer at the negative and positive electrodes, and charge-transfer resistance acting equivalently as electric resistance when a reaction current is generated at an interface of the active material.
- Resistance R has a characteristic which varies with ⁇ 1 , ⁇ 2 , and the battery's temperature. In other words, resistance R can be represented as a function of ⁇ 1 , ⁇ 2 , and battery's temperature.
- the limit lithium concentration is an upper limit value of a lithium concentration in the positive/negative electrodes.
- FIG. 3 conceptually represents a characteristic of how open circuit voltage varies as local SOC varies.
- the rechargeable lithium ion battery has open circuit voltage OCV represented as a difference in potential between the positive electrodes open circuit potential U 1 and the negative electrode's open circuit potential U 2 .
- the positive electrode's open circuit potential U 1 has a characteristic varying with local SOC ⁇ 1 obtained at a surface of the active material of the positive electrode
- the negative electrode's open circuit potential U 2 has a characteristic varying with local SOC ⁇ 2 obtained at a surface of the active material of the negative electrode.
- the initial state means a state in which the rechargeable lithium ion battery is not degraded, and for example means a state of the rechargeable lithium ion battery immediately after the battery is produced.
- the rechargeable lithium ion battery's open circuit voltage OCV has a characteristic decreasing as the battery is electrically discharged. Furthermore, the rechargeable lithium ion battery in a degraded state has voltage decreased in a larger amount than in the initial state for the same electrically discharging period of time. This indicates that as the rechargeable lithium ion battery degrades, its full charge capacity is reduced and its open circuit voltage characteristic has varied.
- the variation of the open circuit voltage characteristic of the rechargeable lithium ion battery that accompanies the battery's degradation is modeled as two phenomena believed to occur in the rechargeable lithium ion battery in a degraded state. These two phenomena are reduction in a single electrode's capacity at the positive/negative electrodes, and a deviation of a correspondence in composition between the positive electrode and the negative electrode.
- Reduction in a single electrode's capacity represents reduction in an ability to accept lithium in each of the positive electrode and the negative electrode. That the ability to accept lithium is decreasing means that the active material and the like that function effectively for electrically charging/discharging the battery is decreasing.
- FIG. 4 is a graph schematically showing how a single electrode's open circuit potential varies as its capacity decreases.
- the positive electrode When the positive electrode has a reduced ability to accept lithium, the positive electrode's capacity corresponding to local SOC ⁇ 1 varies from Q_H 11 to Q_H 12 . Furthermore, when the negative electrode has a reduced ability to accept lithium the negative electrode's capacity corresponding to SOC ⁇ 2 varies from Q_H 21 to Q_H 22 .
- FIG. 5 is a conceptual diagram schematically representing a relationship between a deviation of a correspondence in composition between the positive electrode and the negative electrode, and their open circuit potentials.
- a deviation of a correspondence in composition indicates that when a set of a positive electrode and a negative electrode is used to electrically charge/discharge a rechargeable lithium ion battery the positive electrode's composition ( ⁇ 1 ) and the negative electrode's composition ( ⁇ 2 ) in combination have a deviation from the initial state of the battery.
- Single electrodes' respective compositions ⁇ 1 , ⁇ 2 and open circuit potentials U 1 , U 2 have a relationship represented by a curve similar to that represented in FIG. 3 .
- the axis of the negative electrode's composition ⁇ 2 will shift by ⁇ 2 in a direction in which the positive electrode's composition ⁇ 1 decreases.
- the negative electrode's composition 82 and the negative electrode's open circuit potential U 2 have a relationship represented by a curve shifted in a direction in which the positive electrode's composition ⁇ 1 decreases relative to a curve in the initial state by ⁇ 2 .
- the negative electrode's composition corresponding to the positive electrode's composition ⁇ 1 fix with the rechargeable lithium ion battery in the initial state will be “ ⁇ 2 fix _ini”, and once the rechargeable lithium ion battery has been degraded it will be “ ⁇ 2 fix ”. Note that in FIG. 5 the negative electrode's composition ⁇ L 2 represented in FIG. 3 is 0, which represents that the negative electrode's lithium has all been drawn out.
- the present embodiment introduces the above three degradation parameters of the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and an amount of deviation ⁇ Qs of a correspondence in composition between positive and negative electrodes to model the above two degradation phenomena.
- the positive electrode's capacity ratio k 1 is defined by a ratio of the positive electrode's capacity in a degraded state to that in an initial state, as described above.
- the positive electrode's capacity Q 1 _ini can be previously obtained through an experiment.
- the negative electrode's capacity ratio k 2 is defined by a ratio of the negative electrode's capacity in a degraded state to that in the initial state, as described above.
- the negative electrode's capacity Q 2 _ini can be previously obtained through an experiment.
- FIG. 6 is a schematic diagram for illustrating a deviation of a correspondence in composition caused by degradation.
- the negative electrode with its composition ⁇ 2 of 1 When the rechargeable lithium ion battery is degraded, the negative electrode with its composition ⁇ 2 of 1 will have a capacity of Q 2 _ini ⁇ Q 2 . Furthermore, the positive electrode and the negative electrode have their respective compositions having a correspondence with a deviated capacity ⁇ Qs which is a capacity corresponding to an amount of deviation ⁇ 2 of the axis for the negative electrode's composition relative to that for the positive electrode's composition.
- ⁇ Qs a capacity corresponding to an amount of deviation ⁇ 2 of the axis for the negative electrode's composition relative to that for the positive electrode's composition.
- the positive electrode's composition ⁇ 1 fix _ini corresponds to the negative electrode's composition ⁇ 2 fix _ini.
- the positive electrode's composition ⁇ 1 fix corresponds to the negative electrode's composition ⁇ 2 fix .
- the deviation of the correspondence in composition is with reference to the positive electrode's composition ⁇ 1 fix in the initial state. That is, the positive electrode's compositions ⁇ 1 fix and ⁇ 1 fix _ini are equal in value.
- Expression (8) has a meaning, as described hereinafter.
- the positive electrode's composition ⁇ 1 varies (or is reduced) from 1 to ⁇ 1 fix
- the positive electrode discharges lithium in an amount represented by the following expression (9):
- 1 ⁇ 1 fix has a value indicating how much the positive electrode's composition varies as the rechargeable lithium ion battery is degraded
- k 1 ⁇ Q 1 _ini has a value indicating the positive electrode's capacity after the rechargeable lithium ion battery is degraded.
- k 2 ⁇ Q 2 _ini has a value representing the negative electrode's capacity after the rechargeable lithium ion battery is degraded.
- the amount of deviation ⁇ 2 of the correspondence in composition can be represented by expression (6), using deviated capacity ⁇ Qs of the correspondence in composition.
- the negative electrode's composition ⁇ 2 fix is represented by the above expression (8).
- open circuit voltage OCV is represented as a potential difference between the positive electrode's open circuit potential U 11 and the negative electrode's open circuit potential U 22 in the degraded state. That is, estimating three degradation parameters k 1 , k 2 , ⁇ Qs allows the negative electrode's open circuit potential U 22 with the rechargeable lithium ion battery in a degraded state to be determined, and open circuit voltage OCV can be calculated as a potential difference between the negative electrode's open circuit potential U 22 and the positive electrode's open circuit potential U 11 .
- degradation parameters k 1 , k 2 , and ⁇ Qs are used to estimate the rechargeable lithium ion battery's internal state, more specifically, whether the rechargeable lithium ion battery is degraded as lithium deposits.
- a rechargeable lithium ion battery's degradation includes that attributed to deposition of lithium and that attributed to wear, and distinguishing these types of degradation and thus determining (or estimating) them allows a state of degradation to be determined in detail.
- Degradation attributed to wear means that as a battery electrically conducts or is left or the like its positive and negative electrodes performance (or ability to accept lithium) is impaired, and for example, it includes that the positive/negative electrodes have their active materials worn. Furthermore, a deviated capacity resulting from a coating or the like provided on a surface of an active material (or degradation in composition between the positive electrode and the negative electrode) is also indicated as an example of degradation attributed to wear. On the other hand, degradation attributed to deposition of lithium indicates that the lithium ions used for a battery's reaction change into a byproduct (mainly, metallic lithium), and thus no longer contribute to cell reaction.
- a byproduct mainly, metallic lithium
- open circuit voltage OCV When the rechargeable lithium ion battery is not degraded, open circuit voltage OCV will coincide with that of the rechargeable lithium ion battery in the initial state. That is, when the positive electrodes capacity ratio k 1 and the negative electrode's capacity ratio k 2 are 1 and deviated capacity ⁇ Qs of the correspondence in composition is 0, open circuit voltage OCV calculated (or estimated) as described above will coincide with a value of open circuit voltage OCV (as measured) that is obtained when the rechargeable lithium ion battery is in the initial state (or unused).
- FIG. 7 shows a relationship between the rechargeable lithium ion battery's capacity (SOC) and open circuit voltage OCV (i.e., an open circuit voltage characteristic).
- SOC rechargeable lithium ion battery's capacity
- OCV open circuit voltage characteristic
- a curve shown in FIG. 7 and the like that represents an open circuit voltage characteristic will also be referred to as an “open circuit voltage curve.”
- a dotted line indicates an open circuit voltage curve (as measured)
- a solid line indicates an open circuit voltage curve (as estimated).
- the open circuit voltage curve (as estimated) overlaps the open circuit voltage curve (as measured).
- the axis of ordinate represents open circuit voltage OCV
- the axis of abscissa represents the rechargeable lithium ion battery's capacity.
- FIG. 8 shows a dotted line, which indicates a result of having measured an open circuit voltage curve (as measured) of a rechargeable lithium ion battery degraded only by deposition of lithium, that is, a rechargeable lithium ion battery free of degradation attributed to wear.
- the rechargeable lithium ion battery is held at low temperature, degradation attributed to wear can be suppressed, and this allows deposition of lithium to be alone caused while degradation attributed to wear is suppressed.
- a temperature set to set the rechargeable lithium ion battery at low temperature can be determined. This allows degradation attributed to deposition of lithium to be alone caused in the rechargeable lithium ion battery.
- FIG. 8 represents open circuit voltage (as measured) OCV and open circuit voltage (as estimated) OCV substantially coinciding with each other.
- This open circuit voltage curve (as estimated) is determined with degradation parameters as follows: the positive electrode's capacity ratio k 1 of 1; the negative electrode's capacity ratio k 2 of 1; and the compositions having a correspondence with deviated capacity ⁇ Qs of 062.
- These degradation parameter values can be obtained by searching for and obtaining the three degradation parameters (k 1 , k 2 , ⁇ Qs) allowing the open circuit voltage curve (as estimated) to substantially coincide with the open circuit voltage curve (as measured) represented in FIG. 8 .
- FIG. 9 indicates a result of having measured an open circuit voltage curve (as measured) of a rechargeable lithium ion battery degraded by wear alone, that is, a rechargeable lithium ion battery which does not have lithium deposited therein.
- the axis of ordinate represents open circuit voltage OCV
- the axis of abscissa represents the rechargeable lithium ion battery's capacity.
- a temperature set to set the rechargeable lithium ion battery at high temperature can be determined.
- the temperature set can be 50° C., for example. This allows degradation attributed to wear to be alone caused in the rechargeable lithium ion battery.
- FIG. 9 represents open circuit voltage (as measured) OCV and open circuit voltage (as estimated) OCV substantially coinciding with each other.
- an open circuit voltage curve (as estimated) is determined with degradation parameters as follows: the positive electrode's capacity ratio k 1 of 0.85; the negative electrode's capacity ratio k 2 of 0.97; and the compositions having a correspondence with deviated capacity ⁇ Qs of 0.05.
- These degradation parameter values can be obtained by searching for and obtaining the three degradation parameters (k 1 , k 2 , ⁇ Qs) allowing the open circuit voltage curve (as estimated) to substantially coincide with the open circuit voltage curve (as measured) represented in FIG. 9 .
- the rechargeable lithium ion battery degraded only by wear has the three degradation parameters (k 1 , k 2 , ⁇ Qs) all deviating from those of the rechargeable lithium ion battery unused (or in the initial state). Note that degradation attributed to wear provides the compositions with a correspondence therebetween having a deviated capacity ⁇ Qs smaller than degradation attributed to deposition of lithium does.
- Lithium may deposit because, for example, lithium ions discharged from the positive electrode in electrically charging the battery may not be taken into the negative electrode.
- the positive electrode and the negative electrode will have their compositions with a correspondence having a deviation, and deviated capacity ⁇ Qs will vary.
- deposition of lithium caused alone does not impair the positive and negative electrodes' ability to accept lithium, and accordingly, the positive electrode's capacity ratio k 1 and the negative electrode's capacity ratio k 2 will each be held at 1.
- deviated capacity ⁇ Qs includes a deviated capacity ⁇ Qs(Li) resulting from degradation attributed to deposition of lithium, and a deviated capacity ⁇ Qs(W) resulting from degradation attributed to wear, and accordingly, separating one from the other allows quantitative estimation of an amount of lithium deposited.
- This map represents a correspondence between the positive and negative electrodes' capacity ratios k 1 and k 2 and the deviated capacity ⁇ Qs of a correspondence in composition when the rechargeable lithium ion battery is degraded by wear alone, and it can be previously created based on a result of an experiment.
- holding the rechargeable lithium ion battery at high temperature can prevent deposition of lithium, and thus allows an experiment to be conducted to cause degradation attributed to wear alone.
- Degradation attributed to wear is advanced gradually to decrease the rechargeable lithium ion battery's capacity (i.e., full charge capacity) gradually by a predetermined amount. Whenever the rechargeable lithium ion battery's capacity is decreased, the rechargeable lithium ion battery's open circuit voltage OCV is measured. This allows data to be obtained that indicates how the rechargeable lithium ion battery varies in open circuit voltage OCV as the rechargeable lithium ion battery varies in capacity when the rechargeable lithium ion battery has its capacity degraded as prescribed (i.e., an open circuit voltage curve (as measured)).
- the rechargeable lithium ion battery has a capacity reaching from 100% to 50%, the capacity is decreased (or degraded) by 5% at a time, and whenever the capacity is decreased, the rechargeable lithium ion battery's open circuit voltage OCV is measured.
- the degradation parameters (the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs) can be searched for for causing open circuit voltage (as estimated) OCV to coincide with open circuit voltage (as measured) OCV obtained for each capacity degradation.
- the map (hereinafter also referred to as a map for degradation attributed to wear) shown in FIG. 10 can be obtained.
- the FIG. 10 map shows a correspondence between the positive and negative electrodes capacity ratios k 1 and k 2 and deviated capacity ⁇ Qs(W), and for example, the positive electrode's capacity ratio k 1 and the negative electrode's capacity ratio k 2 can be selected to determine deviated capacity ⁇ Qs(W) resulting from degradation attributed to wear.
- the map can be stored in a memory.
- obtaining data indicating how rechargeable lithium ion battery 10 subject to determination of degradation as shown in FIG. 1 , varies in open circuit voltage (as measured) OCV as the battery varies in capacity (i.e., an open circuit voltage curve), as shown in FIG. 7 to FIG. 9 , allows degradation parameters (k 1 , k 2 , ⁇ Qs) to be searched for so that open circuit voltage (as estimated) OCV may coincide with open circuit voltage (as measured) OCV.
- An open circuit voltage curve can be measured through electrically charging/discharging rechargeable lithium ion battery 10 that has completely been used off board.
- rechargeable lithium ion battery 10 is electrically charged/discharged off board and thus varied in capacity, and in doing so, the battery's voltage and current are also sensed to measure an open circuit voltage characteristic.
- degradation parameter acquisition unit 40 can use the measured open circuit voltage characteristic to search for degradation parameters (k 1 , k 2 , ⁇ Qs) to obtain the positive electrodes capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and battery capacity fluctuation amount (or deviated capacity) ⁇ Qs.
- an open circuit voltage curve by ECU 20 on board when rechargeable lithium ion battery 10 is used.
- the battery's voltage is sensed and how the battery's open circuit voltage varies is measured therefrom, and the battery's current is integrated, and from the integral, how the battery's capacity varies can be measured.
- the measured open circuit voltage curve can be used to allow ECU 20 to search for degradation parameters (k 1 , k 2 , ⁇ Qs).
- battery checker 30 obtains the positive electrodes capacity ratio k 11 , the negative electrode's capacity ratio k 2 , and battery capacity fluctuation amount (or deviated capacity) ⁇ Qs by communicating with ECU 20 .
- Lithium deposition estimation unit 50 refers to the FIG. 10 map for degradation attributed to wear and uses the obtained positive and negative electrodes capacity ratios k 1 and k 2 to calculate deviated capacity ⁇ Qs(W) resulting from degradation attributed to wear. Furthermore, lithium deposition estimation unit 50 subtracts deviated capacity ⁇ Qs(W) from deviated capacity ⁇ Qs that degradation parameter acquisition unit 40 has obtained to calculate deviated capacity ⁇ Qs(Li) resulting from deposition of lithium. Thus, deviated capacity ⁇ Qs can be separated into deviated capacity ⁇ Qs(Li) resulting from deposition of lithium, and deviated capacity ⁇ Qs(W) resulting from degradation attributed to wear. That is, ⁇ Qs(W) corresponds to a “first amount of the battery capacity fluctuation”, and ⁇ Qs(Li) corresponds to a “second amount of the battery capacity fluctuation”.
- FIG. 11 is a flowchart representing a procedure of a process for determining degradation of a rechargeable lithium ion battery according to the present embodiment of the present invention.
- the FIG. 11 flowchart represents a controlling process implemented when for example MPU 31 shown in FIG. 1 executes a program stored previously.
- MPU 31 at Step S 100 obtains a degradation parameter based on an on or off board degradation diagnosis of rechargeable lithium ion battery 10 .
- the degradation diagnosis is based on an open circuit voltage characteristic of rechargeable lithium ion battery 10 ( FIG. 7 to FIG. 9 ).
- the degradation parameter obtained through the degradation diagnosis includes at least the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs. That is, Step S 100 corresponds to a function of degradation parameter acquisition unit 40 described above.
- MPU 31 at Step S 200 uses at least one of the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs(Li) resulting from deposition of lithium to perform a process for determination on the battery's reusability/recyclability.
- MPU 31 at Step S 210 outputs information of determination reflecting the S 200 result as guidance information for reusability/recyclability.
- FIG. 12 specifically illustrates how whether a rechargeable lithium ion battery has a reusable/recyclable negative electrode is determined.
- MPU 31 at Step S 205 reads deviated capacity ⁇ Qs(Li) resulting from deposition of lithium, as obtained at Step S 120 . Then, MPU 31 proceeds to Step S 210 to compare the read ⁇ Qs(Li) with a predetermined determination value Lmax.
- ⁇ Qs(Li) has larger values for lithium deposited in larger amounts. Accordingly, when ⁇ Qs(Li) is determination value Lmax or larger (NO at S 210 ), it can be inferred that lithium deposits on the negative electrode beyond a reusable/recyclable level. Accordingly, MPU 31 proceeds to Step S 250 to determine that the negative electrode is unreusable/unrecyclable.
- MPU 31 determines, in terms of deposition of lithium, that the negative electrode is reusable/recyclable, and accordingly, MPU 31 performs determination based on a still another degradation parameter.
- MPU 31 at Step S 215 reads the negative electrode's capacity ratio k 2 obtained at Step S 100 and MPU 31 at Step S 220 compares the negative electrode's capacity ratio k 2 with a determination value k 2 min.
- the negative electrode's capacity ratio k 2 is determination value k 2 min or smaller (NO at S 220 )
- MPU 31 determines, in terms of deposition of lithium and the negative electrodes capacity, that the negative electrode is reusable/recyclable, and accordingly, MPU 31 performs determination based on a still another degradation parameter.
- MPU 31 at Step S 225 further reads diffusion coefficient Ds and also compares diffusion coefficient Ds with a determination value Dsmin.
- Diffusion coefficient Ds is acquirable for example by using the same technique as described in PTL 3.
- Step S 250 determines that the negative electrode is unreusable/unrecyclable.
- MPU 31 proceeds to Step S 240 .
- MPU 31 at Step S 240 determines that the negative electrode is reusable/recyclable. Note that in the FIG. 12 determination of whether the negative electrode is reusable/recyclable essentially requires the determination done at Steps S 205 and S 210 using deviated capacity ⁇ Qs(Li) resulting from deposition of lithium. On the other hand, the determination based on the negative electrode's capacity ratio k 2 (Steps S 215 , S 220 ) and/or the determination based on diffusion coefficient Ds (Step S 225 , S 230 ) can be omitted.
- FIG. 12 flowchart allows an amount of lithium deposited or furthermore the negative electrode's capacity ratio to be used to determine whether rechargeable lithium ion battery 10 has a reusable/recyclable negative electrode. Furthermore, the diffusion coefficient can also be used to determine whether the battery has a reusable/recyclable negative electrode.
- FIG. 13 is a flowchart specifically showing a procedure of a controlling process for determining whether a rechargeable lithium ion battery has a reusable/recyclable positive electrode.
- MPU 31 at Step S 255 reads the positive electrode's capacity ratio k 1 obtained at Step S 100 , and MPU 31 at Step S 260 compares the positive electrode's capacity ratio k 1 with a determination value k 1 min. Then, when the positive electrodes capacity ratio k 1 is equal to or smaller than determination value k 1 min (NO at S 260 ), MPU 31 determines that the positive electrode's capacity is decreased beyond a reusable/recyclable level, and MPU 31 proceeds to Step S 290 .
- MPU 31 When the positive electrode's capacity ratio k 1 is larger than determination value k 1 min, (YES at S 260 ) MPU 31 performs determination based on a still another degradation parameter. For example MPU 31 at Step S 265 further reads diffusion coefficient Ds and at Step S 270 compares diffusion coefficient Ds with determination value Dsmin.
- Step S 290 determines that the positive electrode is unreusable/unrecyclable.
- MPU 31 proceeds to Step S 280 .
- MPU 31 at Step S 280 determines that the positive electrode is reusable/recyclable. Note that the determination based on diffusion coefficient Ds (Steps S 265 , S 270 ) may be omitted.
- the FIG. 13 flowchart allows the positive electrode's capacity ratio to be used to determine whether rechargeable lithium ion battery 10 has a reusable/recyclable positive electrode. Furthermore, the diffusion coefficient can also be used to determine whether the battery has a reusable/recyclable positive electrode.
- determination values Lmax, k 1 min, k 2 min, and Dsmin can each be set to have different values between determination for recyclability and that for reusability. That is, these determination values can each be defined to have a plurality of thresholds to allow a similar process to be performed to determine reusability/recyclability for each threshold.
- the FIG. 12 and FIG. 13 controlling process can be used for one or both of determination for recyclability and that for reusability.
- the present embodiment allows the determination of degradation of a rechargeable lithium ion battery, based on parameter ⁇ Qs(Li) that reflects an amount of lithium deposited, to determine whether the rechargeable lithium ion battery is recyclable and/or reusable.
- parameter ⁇ Qs(Li) can be calculated without disassembling a cell and conducting a chemical analysis and whether a rechargeable lithium ion battery is reusable can nondestructively be determined appropriately.
- whether a positive electrode is recyclable and whether a negative electrode is recyclable can be determined individually, and determination for recyclability aiming at material recovery through cell disassembly can thus further be useful.
- FIG. 14 is a table for illustrating an example in a system for determining degradation of a rechargeable lithium ion battery to determine whether the battery is reusable according to the present embodiment of the present invention.
- FIG. 14 shows a case in which for example the determination values shown in FIG. 12 and FIG. 13 are provided to have two thresholds to provide three degradation levels to determine reusability.
- a determination result “C” indicates an unreusable/unrecyclable degradation level
- determination results “B” and “A” indicate reusable/recyclable degradation levels.
- the determination result “A” indicates less degradation than the determination result “B”, and indicates that degradation is not advanced.
- Rechargeable lithium ion battery 10 that is reusable is subdivided by a grade I corresponding to a less degraded level and allowing the battery to be reused for a relatively long period of time and a grade II allowing the battery to be reused for a period of time shorter than grade I.
- the positive electrode and the negative electrode both receive the determination result “A” it is determined that the battery is reusable at grade I, whereas when at least one of the electrodes receives determination result “B” it is determined that the battery is reusable at grade II.
- the present embodiment allows the determination of degradation of a rechargeable lithium ion battery to be determined such that the positive electrode's reusability/recyclability and the negative electrode's reusability/recyclability can individually be determined to allow more precise determination on reusability/recyclability than conventional.
- an open circuit voltage characteristic of rechargeable lithium ion battery 10 subject to determination of degradation is measured on board or off board to obtain degradation parameters, or the positive electrodes capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and battery capacity fluctuation amount (or deviated capacity) ⁇ Qs.
- FIG. 15 is a block diagram indicating a system for measuring the open circuit voltage characteristic of rechargeable lithium ion battery 10 of board.
- Rechargeable lithium ion battery 10 has positive and negative electrodes electrically connected to test terminals 35 and 36 shown in FIG. 1 via terminals 11 and 12 shown in and FIG. 1 .
- rechargeable lithium ion battery 10 is connected to a power supply 41 electrically charged and discharged off board and a load 42 via switches 37 and 38 .
- Load 42 receives electric power discharged from rechargeable lithium ion battery 10 .
- power supply 41 supplies electric power to electrically charge rechargeable lithium ion battery 10 .
- MPU 31 can control switches 37 and 38 to control electrically discharging and charging rechargeable lithium ion battery 10 .
- FIG. 15 system is configured such that rechargeable lithium ion battery 10 is connected to load 42 and power supply 41 as switches 37 and 38 are switched on/off as controlled
- the FIG. 15 configuration is not the only configuration to measure an open circuit voltage characteristic off board. That is, any configuration is applicable that can electrically charge and discharge rechargeable lithium ion battery 10 , as intended, to vary its capacity.
- rechargeable lithium ion battery 10 is an in-vehicle battery pack mounted in a hybrid vehicle (HV), a fuel cell vehicle, an electric vehicle (EV), or a similar electrically powered vehicle
- HV hybrid vehicle
- EV electric vehicle
- an inverter can be used as load 42 .
- the inverter receives direct current electric power from the battery pack and converts it into alternating current electric power, and supplies it to a motor/generator which generates kinetic energy to cause the vehicle to travel.
- the battery packs available capacity is reduced and subsequently the battery pack is removed from the vehicle and subsequently the FIG. 15 system can be used to measure open circuit voltage of rechargeable lithium ion battery 10 off board.
- Current sensor 15 a , voltage sensor 15 b , and temperature sensor 15 c sense the rechargeable lithium ion battery 10 current, voltage and temperature, respectively, and output sensed results to MPU 31 .
- Current sensor 15 a , voltage sensor 15 b , and temperature sensor 15 c configure battery sensor 15 shown in FIG. 1 .
- Connecting rechargeable lithium ion battery 10 to power supply 41 allows the rechargeable lithium ion battery 10 open circuit voltage OCV to be measured while varying rechargeable lithium ion battery 10 in capacity (SOC). This can provide data indicating how rechargeable lithium ion battery 10 varies in open circuit voltage (as measured) OCV as the battery varies in capacity (i.e., an open circuit voltage curve).
- FIG. 16 is a flowchart showing a controlling process procedure performed by MPU 31 for obtaining a degradation parameter of a rechargeable lithium ion battery off board.
- FIG. 16 is equivalent to a specific embodiment of Step S 100 of FIG. 11 in obtaining a degradation parameter off board.
- MPU 31 at Step S 301 measures open circuit voltage (as measured) OCV of rechargeable lithium ion battery 10 subject to determination of degradation, based on an output of voltage sensor 15 b . Specifically, measuring open circuit voltage (as measured) OCV while electrically charging/discharging rechargeable lithium ion battery 10 allows an open circuit voltage curve (as measured) to be obtained.
- MPU 31 at Step S 302 appropriately modifies three degradation parameters (the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs) and thus determines whether open circuit voltage (as estimated) OCV determined by the three degradation parameters coincide with open circuit voltage (as measured) OCV obtained at Step S 301 .
- FIG. 17 shows an example of a relationship between open circuit voltage (as estimated) OCV represented by a dotted line and open circuit voltage (as measured) OCV represented by a solid line.
- MPU 31 at Step S 302 determines the degradation parameters when open circuit voltage (as estimated) OCV coincides with open circuit voltage (as measured) OCV.
- the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs are thus determined. Note that deviated capacity ⁇ Qs determined at Step S 302 is deviated capacity ⁇ Qs obtained when degradation attributed to deposition of lithium and degradation attributed to wear are both present.
- open circuit voltage (as estimated) OCV does not completely coincide with open circuit voltage (as measured) OCV, setting a range in which they are regarded as coinciding with each other (i.e., a tolerable error) allows whether open circuit voltage (as estimated) OCV and open circuit voltage (as measured) OCV coincide with each other to be determined.
- MPU 31 at Step S 303 uses the positive and negative electrodes' capacity ratios k 1 and k 2 determined at Step S 302 and the map for degradation attributed to wear (see FIG. 10 ) to determine deviated capacity ⁇ Qs(W). Furthermore, MPU 31 at Step S 304 obtains a difference between deviated capacity ⁇ Qs obtained at Step S 302 and deviated capacity ⁇ Qs(W) obtained at Step S 303 . This calculates deviated capacity ⁇ Qs(Li) resulting from degradation attributed to deposition of lithium.
- an open circuit voltage characteristic of rechargeable lithium ion battery 10 subject to determination of degradation can be measured off board to obtain degradation parameters, or the positive electrode's capacity ratio k 1 , the negative electrodes capacity ratio k 2 , and deviated capacity ⁇ Qs.
- deviated capacity ⁇ Qs can be separated into deviated capacity ⁇ Qs(W) resulting from degradation attributed to wear and deviated capacity ⁇ Qs(Li) resulting from degradation attributed to deposition of lithium to allow deposition of lithium to be quantitatively estimated without disassembling rechargeable lithium ion battery 10 and conducting a chemical analysis.
- the second embodiment in an exemplary variation provides the process that has been described in the second embodiment (see FIG. 16 ) on board.
- a process similar to that of the second embodiment is performed by a controller (ECU) controlling electrically charging/discharging a rechargeable lithium ion battery mounted in an electrically powered vehicle.
- An electrically powered vehicle which can electrically charge an in-vehicle battery (a rechargeable lithium ion battery) from a power supply external to the vehicle, is used.
- a vehicle includes a plug-in hybrid vehicle (PHV) and an EV.
- FIG. 18 is a flowchart showing a procedure of a controlling process for obtaining a degradation parameter of a rechargeable lithium ion battery that is mounted in a vehicle on board.
- the FIG. 18 process is performed by a controller (ECU 20 indicated in FIG. 1 for example) mounted in a vehicle.
- FIG. 18 is equivalent to a specific embodiment of Step S 100 of FIG. 11 in obtaining degradation parameters on board. That is, in the exemplary variation of the second embodiment, degradation parameter acquisition unit 40 ( FIG. 2 ) has its function partially implemented outside battery checker 30 .
- ECU 20 at Step S 401 measures open circuit voltage (as measured) OCV of rechargeable lithium ion battery 10 and an amount of a current accumulated of the battery, as based on an output of the voltage sensor and that of the current sensor that are included in battery sensor 15 .
- open circuit voltage (as measured) OCV and an amount of a current accumulated are measured, as appropriate, and a curve can thus be obtained that indicates how the batters open circuit voltage (as pleasured) OCV varies as its capacity varies (i.e., an open circuit voltage curve as a measured value).
- ECU 20 at Step S 402 sets (or selects) candidates for degradation parameters the positive electrode's capacity ratio k 1 , the negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs) for determining open circuit voltage (as estimated) OCV.
- the degradation parameters can be set in various methods, preferably, a method is selected for performing an operation process for setting the degradation parameters efficiently.
- a degradation parameter may be selected within, a range which is previously determined through an experiment or the like and in which degradation attributed to wear and degradation attributed to deposition of lithium are actually caused.
- the positive electrode's capacity ratio k 1 and the negative electrode's capacity ratio k 2 depend solely on degradation attributed to wear, and accordingly, the positive electrode's capacity ratio k 1 and the negative electrode's capacity ratio k 2 can be varied within a range within which degradation attributed to wear is actually caused.
- ECU 20 at Step S 403 uses the degradation parameters set at Step S 402 to calculate a characteristic indicating how open circuit voltage (as estimated) OCV varies as the capacity varies (i.e., an open circuit voltage curve as an estimated value).
- ECU 20 at Step S 404 calculates an error between the open circuit voltage curve (as estimated) calculated at Step S 403 and the open circuit voltage curve (as measured) obtained at Step S 401 .
- This error includes a voltage error and a capacity error.
- a voltage error ⁇ V (see FIG. 19 ) can be calculated specifically by comparing the open circuit voltage curve (as estimated) and the open circuit voltage curve (as measured).
- Voltage error ⁇ V may be a voltage error in a specific battery capacity, or may be an average of voltage errors between two open circuit voltage curves.
- a capacity error ⁇ Q can be obtained for example in a method described hereinafter.
- the open circuit voltage curve (as estimated) is used to calculate a capacity Q 1 between an open circuit voltage before the battery is electrically charged and an open circuit voltage after the battery is electrically charged.
- a current is sensed and accumulated in value, and a charged capacity Q 2 can be calculated therefrom.
- an absolute value of capacity error ⁇ Q (
- rechargeable lithium ion battery 10 will be relaxed, and accordingly there is no difference in concentration of lithium and open circuit voltage can accurately be measured.
- Rechargeable lithium ion battery 10 is relaxed for example when a vehicle is stopped beyond a predetermined period of time.
- open circuit voltage (as measured) OCV of the rechargeable lithium ion battery for when the battery has a specific capacity can be obtained.
- the specific open circuit voltage measured for the specific capacity allows an open circuit voltage (as measured) to be compared with an open circuit voltage curve (as estimated) to obtain voltage error ⁇ V, as shown in FIG. 20 . Furthermore, if a plurality of open circuit voltages (as measured) are measured, capacity error ⁇ Q can be obtained as described above. Specifically, an open circuit voltage curve (as estimated) is used to calculate capacity Q 1 between open circuit voltages of two points (as measured). Furthermore, measuring a value of an accumulated current when the open circuit voltages (as measured) of the two points are obtained allows the value to be used to calculate capacity Q 2 . Then, a difference of capacity Q 1 and capacity Q 2 (
- ECU 20 at Step S 405 calculates an evaluation function f ( ⁇ V, ⁇ Q) for voltage error ⁇ V and capacity error ⁇ Q obtained at Step S 404 .
- evaluation function f ( ⁇ V, ⁇ Q) voltage error ⁇ V and capacity error ⁇ Q with a weight added thereto can be used.
- ECU 20 determines whether evaluation function f ( ⁇ V, ⁇ Q) calculated from the currently set degradation parameters is smaller than evaluation function f ( ⁇ V, ⁇ Q) calculated from the immediately previously set degradation parameters.
- evaluation function f ( ⁇ V, ⁇ Q) calculated from the currently set degradation parameters is smaller than evaluation function f ( ⁇ V, ⁇ Q) calculated from the immediately previously set degradation parameters.
- the former is stored to a memory. If the current evaluation function f ( ⁇ V, ⁇ Q) is larger than the immediately previous evaluation function f ( ⁇ V, ⁇ Q), the latter will remain stored in the memory.
- ECU 20 at Step S 406 determines whether each degradation parameter has been varied throughout a search range, and if so, ECU 20 proceeds to Step S 407 . Otherwise, ECU 20 returns to Step S 402 .
- Steps S 402 -S 406 are repeated until each degradation parameter has been varied throughout a search range. Then, evaluation function f ( ⁇ V, ⁇ Q) that serves as a minimum value is determined and an open circuit voltage curve for which this evaluation function (or the minimum value) is obtained can be determined, and the degradation parameters (k 1 , k 2 , ⁇ Qs) defining an open circuit voltage curve (as estimated) can be determined. Determining degradation parameters allowing an evaluation function to indicate a minimum value allows a degraded state (i.e., degradation attributed to wear and degradation attributed to deposition of lithium) to be determined more precisely.
- deviated capacity ⁇ Qs that is determined includes deviated capacity ⁇ Qs(W) by degradation attributed to wear, and deviated capacity ⁇ Qs(Li) by degradation attributed to deposition of lithium.
- ECU 20 at Step S 407 uses degradation parameters determined through Steps S 402 -S 406 (i.e., the positive electrode's capacity ratio k 1 and the negative electrode's capacity ratio k 2 ) and the map for degradation attributed to wear (see FIG. 10 ) to determine deviated capacity ⁇ Qs(W) resulting from degradation attributed to wear.
- ECU 20 at Step S 408 calculates a difference between deviated capacity ⁇ Qs determined through Steps S 402 -S 406 and deviated capacity ⁇ Qs(W) obtained at Step S 407 to calculate deviated capacity ⁇ Qs(Li) attributed to deposition of lithium.
- the second embodiment in the exemplary variation allows a rechargeable lithium ion battery mounted in an electrically powered vehicle to be diagnosed for degradation, as based on an open circuit voltage characteristic, to obtain a positive electrode's capacity ratio k 1 , a negative electrode's capacity ratio k 2 , and deviated capacity ⁇ Qs on board.
- the degradation parameters can be obtained on board based on an open circuit voltage characteristic for both PHV and EV having a function using a power supply external to the vehicle to externally electrically charge an in-vehicle battery, and a hybrid vehicle which is not equipped with the function.
- the obtained degradation parameters can be used to quantitatively estimate deposition of lithium without disassembling rechargeable lithium ion battery 10 and conducting a chemical analysis.
- the function of degradation parameter acquisition unit 40 indicated in FIG. 2 in obtaining the degradation parameters off board can be implemented by the battery checker 30 MPU 31 , whereas that in obtaining the degradation parameters on board can partially be implemented by an ECU mounted in the vehicle (for example, ECU 20 of FIG. 1 ).
- Step S 200 determination unit 60 of FIG. 1
- Step S 200 determination unit 60 of FIG. 1
- FIG. 21 represents a process procedure for illustrating an additional example of determining whether a rechargeable lithium ion battery is reusable in determining degradation of the battery according to the third embodiment of the present invention.
- FIG. 21 represents a controlling process that can be additionally performed for the determination process performed in the first embodiment.
- MPU 31 at Step S 150 confirms whether rechargeable lithium ion battery 10 is reusable. If not (NO at S 500 ), the following process is not performed.
- MPU 31 at Step S 510 determines whether ⁇ Qs(Li) and ⁇ Qs(W) have a difference larger than a determination value Qth. That is, MPU 31 at Step S 510 determines which one of a deviated capacity resulting from degradation attributed to wear and a deviated capacity resulting from deposition of lithium is a dominant factor of overall deviated capacity ⁇ Qs of rechargeable lithium ion battery 10 .
- MPU 31 at Step S 515 determines what relationship ⁇ Qs(Li) and ⁇ Qs(W) have therebetween in magnitude. For ⁇ Qs(Li)> ⁇ Qs(W) (YES at S 515 ), MPU 31 proceeds to Step S 520 to set an application code at “1”. In contrast, for ⁇ Qs(W)> ⁇ Qs(Li) (NO at S 515 ) MPU 31 proceeds to Step S 530 to set the application code at “2”.
- the application code represents a climate condition that is preferable in reusing rechargeable lithium ion battery 10 .
- Rechargeable lithium ion battery 10 having ⁇ Qs(Li) ⁇ Qs(W)>Qth and degraded dominantly by deposition of lithium is given the application code “1” indicating that the battery is suitable for being used at high temperature, since deposited lithium has such a tendency that when it is held at high temperature for a long period of time it is recoverable to lithium that can again contribute to cell reaction. Then, rechargeable lithium ion battery 10 given the application code “1” is mounted for example in a vehicle having a radiator with a capacity set to be larger than normal for a tropical area.
- rechargeable lithium ion battery 10 having ⁇ Qs(W) ⁇ Qs(Li)>Qth and degraded dominantly through wear is given the application code “2” indicating that the battery is suitable for being used at low temperature, since degradation attributed to wear is easily caused when the battery is used at high temperature, and it is less easily caused when the battery is used at low temperature. Then, rechargeable lithium ion battery 10 given the application code “2” is mounted for example in a vehicle having mounted therein a larger number of accessory batteries than normal for a cold district.
- the FIG. 21 determination of degradation of a rechargeable lithium ion battery allows deviated capacity ⁇ Qs of rechargeable lithium ion battery 10 (battery capacity fluctuation amount) to be separated into amount ⁇ Qs(W) resulting from degradation attributed to wear and amount ⁇ Qs(Li) resulting from deposition of lithium to further provide determination information indicating a climate condition suitable for reuse.
- FIG. 22 is a flowchart showing a procedure of a controlling process in determining degradation of a rechargeable lithium ion battery to determine whether the battery has a recyclable negative electrode according to the third embodiment.
- MPU 31 performs steps S 205 and S 210 similar to FIG. 12 , and when ⁇ Qs(Li) is equal to or larger than a determination value LRCmax (NO at S 210 ), MPU 31 proceeds to Step S 212 to set on a flag FRM.
- MPU 31 can perform Steps S 215 , S 220 and/or Steps S 225 , S 230 similarly as done in FIG. 12 to compare the negative electrode's capacity ratio k 2 and/or the negative electrode's diffusion coefficient Ds with a determination value to determine recyclability.
- Steps S 220 and S 230 are also performed with determination values k 2 RCmin and DsRCmin involved in determining recyclability. If the negative electrode's capacity ratio k 2 or diffusion coefficient Ds is a determination value or smaller (NO at S 220 or S 230 ), MPU 31 skips Step S 212 .
- Step S 230 i.e., when a degradation parameter including deviated capacity ⁇ Qs(Li) resulting from deposition of lithium does not have a degradation level having a determination value or larger MPU 31 proceeds to Step S 240 and determines that the negative electrode's material is recyclable.
- MPU 31 determines at Step S 235 whether flag FRM is set on.
- Step S 245 determines that the negative electrode is recyclable after it has lithium removed therefrom.
- Step S 245 is skipped.
- Lithium metal is dissolvable in water or the like, and a lithium removal process to dissolve lithium in a solvent can remove lithium to allow the negative electrode's material to be recycled. Accordingly, rechargeable lithium ion battery 10 degraded by excessive lithium deposition can additionally be subjected to the lithium removal process to provide a possibility that the negative electrode's material may be recycled.
- the FIG. 22 determination of degradation of a rechargeable lithium ion battery and determination of whether its negative electrode's material is recyclable, that is additionally provided with a lithium removal process, allows a recyclable battery to be extracted and can thus further add a recyclable subject. Furthermore, the lithium removal process can be performed less frequently and a simpler and less expensive recycling process can be achieved than when how much lithium is deposited is not considered and rechargeable lithium ion batteries to be recycled are all undergo the lithium removal process.
- rechargeable lithium ion battery 10 subject to determination of degradation is a battery pack mounted in an electrically powered vehicle
- present invention is not limited thereto. That is, a rechargeable lithium ion battery allowing, an open circuit voltage characteristic to be measured therefrom off board and a degradation parameter to be obtained therefrom according to at least the second embodiment can be determined for reusability/recyclability by the determination of degradation that has been described in the first and third embodiments.
- the present invention is applicable to a diagnosis for degradation for determining whether a rechargeable lithium ion battery is reusable/recyclable.
Abstract
Description
- PTL 1: Japanese Patent Laying-Open No, 2003-7348
- PTL 2: Japanese Patent Laying-Open No. 09-232008
- PTL 3: Japanese Patent Laying-Open No. 2008-241246
- PTL 4: Japanese Patent Laying-Open No. 2009-63555
- PTL 5: Japanese Patent Laying-Open No, 2009-199936
V=OCV(θ1,θ2)−R×I (1)
where OCV represents the rechargeable lithium ion battery's open circuit voltage, R represents the rechargeable lithium ion battery's overall resistance, and I represents a current that flows through the rechargeable lithium ion battery. Resistance R includes pure electric resistance against electron transfer at the negative and positive electrodes, and charge-transfer resistance acting equivalently as electric resistance when a reaction current is generated at an interface of the active material.
θi=Cse,i/Cs,i,max (i−1, 2) (2)
where Cse, i represents a lithium concentration (as averaged) at an interface of the active material (of the positive or negative electrode), and Cs, i, max represents a limit lithium concentration in the active material (of the positive or negative electrode). The limit lithium concentration is an upper limit value of a lithium concentration in the positive/negative electrodes.
k1=(Q1— ini−ΔQ1)/Q1— ini
wherein 0<k1<1 (3),
where Q1_ini represents the positive electrodes capacity with the rechargeable lithium ion battery in the initial state (Q_H11 represented in
k2=(Q2— ini−ΔQ2)/Q2— ini
wherein 0<k2<1 (4),
where Q2_ini represents the negative electrode's capacity with the rechargeable lithium ion battery in the initial state (Q_H21 represented in
1:Δθ2=(Q2— Ini−ΔQ2):ΔQs (5).
From expression (4) and expression (5), the following expression (6) is obtained:
When the rechargeable lithium ion battery is in the initial state, the positive electrode's composition θ1 fix_ini corresponds to the negative electrode's composition θ2 fix_ini. When the rechargeable lithium ion battery is in a degraded state, the positive electrode's composition θ1 fix corresponds to the negative electrode's composition θ2 fix. Furthermore, the deviation of the correspondence in composition is with reference to the positive electrode's composition θ1 fix in the initial state. That is, the positive electrode's compositions θ1 fix and θ1 fix_ini are equal in value.
θ1fix=θ1fix — ini (7),
θ2fix=[(1−θ1fix)×k1×Q1— ini−ΔQs]/(k2×Q2— ini) (8).
Expression (8) has a meaning, as described hereinafter. When the rechargeable lithium ion battery degrades, and accordingly, the positive electrode's composition θ1 varies (or is reduced) from 1 to θ1 fix, the positive electrode discharges lithium in an amount represented by the following expression (9):
The positive electrode discharges lithium in an amount=(1−θ1fix)×k1×Q1— ini (9).
Herein, 1−θ1 fix has a value indicating how much the positive electrode's composition varies as the rechargeable lithium ion battery is degraded, and k1×Q1_ini has a value indicating the positive electrode's capacity after the rechargeable lithium ion battery is degraded.
θ2fix=(1−θ1fix)×k1×Q1— ini/(k2×Q2— ini) (10).
Herein, k2×Q2_ini has a value representing the negative electrode's capacity after the rechargeable lithium ion battery is degraded.
θ2fix=(1−θ1fix)×k1×Q1— ini/(k2×Q2— ini)−Δθ2 (11).
The amount of deviation Δθ2 of the correspondence in composition can be represented by expression (6), using deviated capacity ΔQs of the correspondence in composition. Thus the negative electrode's composition θ2 fix is represented by the above expression (8).
Claims (20)
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Also Published As
Publication number | Publication date |
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WO2011155298A1 (en) | 2011-12-15 |
EP2579381A4 (en) | 2015-01-07 |
CN103081212B (en) | 2016-09-21 |
JP2011258337A (en) | 2011-12-22 |
EP2579381B1 (en) | 2016-11-30 |
CN103081212A (en) | 2013-05-01 |
US20130076363A1 (en) | 2013-03-28 |
JP5341823B2 (en) | 2013-11-13 |
EP2579381A1 (en) | 2013-04-10 |
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